The present invention relates to a screening method and a screening prober. More particularly, the present invention relates to a screening method and a screening prober that are used for removing defective semiconductor elements from among the semiconductor elements formed on a semiconductor wafer before electric characteristic tests of various kinds are executed with respect to each of the semiconductor elements. (In the description below, the xe2x80x9csemiconductor waferxe2x80x9d will be referred to simply as a xe2x80x9cwaferxe2x80x9d, and the xe2x80x9csemiconductor elementxe2x80x9d will be referred to as a xe2x80x9cdevicexe2x80x9d.)
Electric characteristic tests are executed with respect to devices before these devices are packaged, i.e., in the state where they are on a wafer. Only those devices that are determined to be good in quality are packaged. Broadly speaking, electric characteristic tests that are executed for devices formed on a wafer are classified into a DC test, AC test and a function test. By these tests, the devices are screened to select good ones. A prober and a tester are employed in the tests. A signal from the tester is supplied to each of the devices on the wafer through the prober. Measurement signals from the devices are supplied to the tester. On the basis of the measurement signals, the tester screens the devices to pick out defective ones.
With the recent development in fine structure working technology, the integration density of devices has been remarkably enhanced, and the devices have a large number of functions. Since the device are large in scale and are highly sophisticated, the inspection for screening the devices to remove defective ones cannot be executed with high efficiency. In other words, the inspection time are very long and the inspection requires high cost. In addition, more and more breakdowns are attributed to such defects as cannot be easily detected in function tests. As a result, even devices that have passed the shipping inspection and are to be shipped as finished products may include a large number of defective ones which are due to the defects of the devices themselves. In addition, the sophistication of devices has resulted in the necessity of using more complicated test patterns, which are difficult to design.
In order to lower the inspect cost and to enhance the breakdown detection rate, attention is paid to technology that enables an IDDQ (IDD quiescent) test, a BIST (a built-in self test), a BISE (built-in self exercise), etc. to be executed with ease. Of these tests, the IDDQ test is a test in which a very small amount of power supply current flowing in a device in the quiescent state is detected by use of different test pattern signals, and the differences among the power supply currents are utilized for the detection of a defect. The IDDQ test can be executed by merely inputting test pattern signals to internal nodes of a device and determining a current value used for the detection of a defect for each of the pattern signals. Even though the IDDQ test uses a small number of test pattern signals, it enables detection of these defects which cannot be detected in the DC test or function test. For example, the IDDQ test enables detection of a short circuit, an open circuit, an insulation failure, etc. Recently, the IDDQ test attracts attention of those skilled in the art since it can supplement the function test.
Unlike the BIST and BISE, the IDDQ test enables a device to be externally inspected without having to incorporate a test circuit in the device. Therefore, the IDDQ test is considered advantageous in that it does not result in an increased device area or a deterioration in the device function. If the IDDQ test is used in an early stage of the test process, defective devices can be picked out by screening, so that the inspection costs that are required for the execution of subsequent tests, including the DC test, the AC test and the function test, can be remarkably lowered.
A problem of the prior art is that if power supply current is kept supplied to a defective device during the screening of devices, an abnormal amount of current flows from the defective device, burning out the measuring system.
Another problem of the prior art is that the number of wires used between the tester and the prober is very large, and the apparatus is inevitably large, accordingly.
An object of the present invention is to provide a solution to at least one of the problems described above.
Another object of the present invention is to prevent a power supply current from flowing to a defective device by providing a current cutoff structure, thereby preventing a measurement system from being burnt out due to an abnormal amount of current which might be generated from the defective device.
A further object of the present invention is to provide a screening method and a screening prober which enable an IDDQ test to be executed on the side of the prober before electric characteristic inspection, including a DC test, an AC test and a function test, is carried out with respect to devices, which helps realize a compact structure and enables a remarkable reduction in the number of wires that must be connected to a control section, and which enables low-cost manufacture of devices.
According to the first aspect of the present invention, there is provided a method used for screening semiconductor devices formed on a semiconductor wafer and comprising:
applying a power supply voltage to a large number of the semiconductor devices;
measuring of a quiescent power supply current which flows in each of the semiconductor devices when the power supply voltage is applied thereto;
determining that each of the semiconductor devices is one of a non-defective device and a defective device based on a value of the quiescent power supply current; and
preventing to apply a power supply voltage to the semiconductor device that is determined to be a defective device.
In the screening method described above, the determining preferably includes:
determining of a setting value;
comparing of the value of the quiescent power supply current with the setting value; and .
determining the semiconductor devices to be defective if values of the quiescent power supply currents flowing through the semiconductor devices are greater than the setting value.
In the screening method described above, the preventing to apply the power supply voltage is preferably followed by:
specifying the semiconductor devices other than those which have been determined to be defective; and
inspecting of electric characteristics of the semiconductor devices that have been specified.
In the screening method described above, the inspecting electric characteristics preferably includes screening based on an IDDQ test.
According to the second aspect of the present invention, there is provided a method used for screening semiconductor devices and comprising:
applying a power supply voltage from a power supply source to a large number of the semiconductor devices by way of an application/measurement module, the power supply source being provided for a control station connected to a main apparatus through the application/measurement module, and semiconductor devices being formed on a semiconductor wafer placed inside the main apparatus;
measuring a quiescent power supply current which flows in each of the semiconductor devices when the power supply voltage is applied thereto, the quiescent power supply current being measured in the application/measurement module;
determining that each of the semiconductor devices is one of a non-defective element and a defective element based on a value of the quiescent power supply current; and preventing to apply the power supply voltage to a semiconductor device that is determined to be a defective device.
In the screening method of the second aspect, the determining preferably includes:
determining a setting value in the application/measurement module;
comparing the value of the quiescent power supply current with the setting value in the application/measurement module; and
determining semiconductor devices to be defective if values of quiescent power supply currents flowing through the semiconductor devices are greater than the setting value in the application/measurement module.
It is preferable that the screening method of the second aspect further includes:
specifying semiconductor devices other than those which have been determined to be defective in the application/measurement module; and
inspecting another electric characteristics of the semiconductor devices that have been specified in the application/measurement module.
In the screening method of the second aspect, the inspecting another electric characteristics preferably includes screening based on an IDDQ test.
In the screening method of the second aspect, the inspecting another electric characteristics preferably includes a process in which at least one of a BIST and a BISE is carried out.
In the screening method of the second aspect, the inspecting another electric characteristics includes bringing the semiconductor devices into simultaneous contact with contactors arranged inside a main apparatus.
In the screening method of the second aspect, the inspecting another electric characteristics is executed by index-feeding the semiconductor wafer with reference to contactors arranged inside a main apparatus.
According to the third aspect of the present invention, there is provided a prober for screening semiconductor devices, which comprises:
a main apparatus including a main chuck on which the semiconductor wafer is placed, and contactors which are brought into electric contact with a large number of semiconductor devices formed on the semiconductor wafer placed on the main chuck;
a power supply, connected to the contactors, for applying voltage to the semiconductor devices through the contactors;
a measured current monitoring apparatus, connected to the semiconductor devices, for measuring quiescent power supply currents that flow through the semiconductor devices when the semiconductor devices are applied with the voltage, and for determining that each of the semiconductor devices is one of a non-defective device and a defective device on the basis of measurement of the quiescent power supply currents; and
a voltage cutoff circuit for cutting off application of the voltage to a semiconductor device that has been determined to a defective element.
In the screening prober of the third aspect, it is preferable that the measured current monitoring apparatus be an apparatus that determines a setting value beforehand, compares the quiescent power supply currents with the setting value, and determines a semiconductor device to be defective if the quiescent power supply current flowing through that semiconductor device is greater than the setting value.
It is preferable that the screening prober of the third aspect further comprise:
an apparatus for specifying semiconductor devices other than those which have been determined to be defective; and
an inspection apparatus for inspecting electric characteristics of the semiconductor devices that have been specified.
In the screening prober of the third aspect, it is preferable that the inspection apparatus execute at least an IDDQ test.
According to the fourth aspect of the present invention, there is provided a prober for screening semiconductor devices, which comprises:
a main apparatus including a main chuck on which a semiconductor wafer is placed, and contactors which are brought into electric contact with a large number of the semiconductor devices formed on the semiconductor wafer placed on the main chuck;
a power supply, connected to the main apparatus, for applying voltage to the semiconductor devices through the contactors;
a measured current monitoring apparatus, connected to the main apparatus, for measuring quiescent power supply currents that flow through the semiconductor devices when the semiconductor devices are applied with the voltage, and for determining that each of the semiconductor devices is one of a non-defective device and a defective device on the basis of measurement of the quiescent power supply currents; and
a cutoff circuit, connected between the power supply and the main apparatus, for cutting off application of power supply voltage to the semiconductor device on the basis of determination made by the measured current monitoring apparatus.
In the screening prober of the fourth aspect, is preferable that the measured-current monitoring apparatus be an apparatus that determines a setting value beforehand, compares the quiescent power supply currents with the setting value, and determines a semiconductor device to be defective if the quiescent power supply current flowing through that semiconductor device is greater than the setting value.
It is preferable that the screening prober of-the fourth aspect further comprise:
an apparatus for specifying semiconductor devices other than those which have been determined to be defective; and
an inspection apparatus for inspecting electric characteristics of the semiconductor devices that have been specified.
In the screening prober of the fourth aspect, it is preferable that the inspection apparatus execute at least an IDDQ test.
In the screening prober of the fourth aspect, it is preferable that the inspection apparatus execute at least one of a BIST and a BISE.
In the screening prober of the fourth aspect, the contactors preferably include a mechanism for enabling simultaneous contact with the semiconductor devices, and the screening prober preferably includes:
a controller for controlling an order in which measurement is made with respect to semiconductor devices which are included among those in contact with the contactors and which have been specified;
a multiplexer, connected between the contactors and the measured-current monitoring apparatus and operating under the controller, for switching the semiconductor devices one to another and sequentially connecting the semiconductor devices to the measured-current monitoring apparatus; and
a measurement result storage apparatus, connected to the measured-current monitoring apparatus, for storing results of measurement obtained by the measured-current monitoring apparatus.
It is preferable that the screening prober of the fourth aspect further comprise:
a pattern storage apparatus for storing test patterns used in the IDDQ test;
a pattern driver, connected to the pattern storage apparatus, for outputting the test pattern signal stored in the pattern storage apparatus; and
a multiplexer for sequentially applying the test pattern signal from the pattern driver to the semiconductor devices that have been specified.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.